You wrote, I don't really think the dollar amount you charge each month matters, nor the percentage of your available credit, through you want to keep it relatively small. The big issue is to establish a history of responsible usage, not volume usage.

The dollar amount matters in so much as it can affect your credit utilization. If you need to buy something that might come close to maxing out your credit line and you want the purchase protections of your card, consider sending the credit card company some of the money in advance.

Also, it's not a history of responsible usage that matters. It's a history of on-time payments and no other negative marks. The balance issue I mentioned before is a transient effect on your credit score and should disappear in 30 days if you pay the account on-time, in full each month.